In the art of dental implantology, abutments have become widely known. They are attached to the dental implant which was previously implanted in a patient's jaw bone. This is normally done by means of a screw joint, wherein torques within the range of 35 Ncm are used to connect the abutment to the dental implant.
In the manufacturing of a prosthesis, supports are frequently used which facilitate three-dimensional modeling of a precisely fitting dental prosthesis. There is the possibility of direct gating at a pre-formed casting abutment which most of the time consists of a gold alloy. This casting abutment is fixed to the implant or the implant analogue, respectively, by means of a screw. For achieving a clean screw channel during subsequent gating, a support, called in the following modeling aid and made of a plastic which can be burnt out, is plugged onto the casting abutment. This modeling aid can be modified as required.
For the manufacturing of the dental model, the desired shape of the individual secondary part is formed with a wax in the area of the collar of the casting abutment and the modeling aid, and subsequently a mold for casting is formed around the wax model according to methods well-known in the art. Then the modeling aid and the wax are burnt out for exposing the structure to be produced or the dental model as a die. A well-known method for producing these dies is lost-wax casting, wherein a die is manufactured, the wax is molten out during the casting process and the modeling aid is burnt without any residue. As a further step, a precious metal alloy is cast into this die through a cast channel, whereupon the highly liquid metal is flowing into the die and is attached to the surface of the casting abutment. At the same time, the die produced by the molten wax model is filled with the wax model copy.
Practice has shown that tightening of the occlusal screw for fixing the casting abutment to the dental model can cause tensions which may lead e.g. to a shift of the modeling aid in the vertical direction. This can cause formation of a gap between the casting abutment and the modeling aid, which gap is filled, during manufacturing of the casting pattern, with the encapsulant surrounding the modeling aid and the casting abutment. During gating, this area is not filled with metal, but remains occupied by the encapsulant so that the finished casting will have a gap, i.e. a casting error.
From SA-2003/9354, an abutment for dental implants is known wherein a (precious) metal cylinder is arranged on a dental implant, on whose occlusal end a plastic sleeve for manufacturing a socket is fastened. On its side facing the metal cylinder, the sleeve has an inner thread engaging a corresponding outer thread on the abutment for enabling casting of a metal post in the metal cylinder of the abutment and around the metal cylinder and for fixing it to the abutment. For a flawless casting process, the threaded joint must have very close tolerances in order to guarantee a very tight closure. In practice, these close tolerances can be achieved by means of fine threads which are, however, costly and very sensitive to handling.